In the conversation, Bezos focused primarily on the ambitions of his rocket company, Blue Origin, and his goal of making space a place where scores of people can live and work.

"The solar system can support a trillion humans," Bezos said. "Then we'd have 1,000 Mozarts and 1,000 Einsteins. Think how incredible and dynamic that civilisation will be."

He acknowledged that that scenario is, of course, a long way off. But he said it's why he founded Blue Origin: The company's immediate goal is to develop reusable rockets, including a system called New Glenn, to dramatically reduce the cost of accessing space.

Bezos thinks that once that's in place, a new era of space entrepreneurship will arrive – something akin to how the internet led to the launch of countless companies.

But when Foust asked about the steps Bezos thinks are required to populate space with millions of people, the billionaire took a jab at his competition.

Why Bezos thinks people who want to settle Mars should try Everest first

Bezos did not name Musk when he talked about settling on Mars. But the two billionaires have a long-running and fairly well-known rivalry. (Musk sometimes replies to questions about Bezos and Blue Origin with "Jeff who?")

The audience Bezos addressed in February – an aviation group called the Wings Club – most likely knew about this simmering competition, because laughter filled the room after Bezos' critical remarks.

Leading up to the Mars-Everest comparison, Bezos said:

"I already talked a little bit about unleashing entrepreneurialism in space, and that is really critical. If you look even further beyond that, or ask a big question – 'Why do we need to go to space? Why do humans need to go to space? What's that all about?' – I think that is a very useful question to ponder.

"My answer is a little different from the answer that I think you hear sometimes more commonly. One thing I find very unmotivating is the kind of 'plan B' argument, where the Earth gets destroyed, where you want to be somewhere else."

That too alluded to a vision Musk has described: using SpaceX, his rocket company, to settle on Mars as quickly as possible, to figuratively "copy" the human race onto a backup drive – just in case anything horrendous befalls our civilisation on Earth.

SpaceX, which declined to comment on Bezos' recent talk, is also working to establishing lower-cost space transportation.

Musk thinks that eventually a Starship could send about 100 people and 150 tons of cargo to Mars at a time, helping to permanently and sustainably settle on the red planet starting in the 2050s.

But as Bezos pointed out, Mars would not be a nice place to live at all. It's also why he called Mount Everest "a garden paradise" compared with the red planet.

Mars, about 158 million miles from Earth, has an atmosphere roughly 1 percent as dense as Earth's at the surface. That makes the planet a veritable vacuum chamber – spacesuits would be required for any journey outside.

At the top of Mount Everest, air pressure is about 33 percent of what it is at sea level. That's enough to get by without a spacesuit, though supplemental oxygen is usually required.

It's also far colder on Mars, which has an average global temperature of -81 degrees Fahrenheit (-62 degrees C).

There's also the issue of radiation exposure on Mars. If a person were to spend a year on the red planet's surface, they would receive about 234 millisieverts of radiation exposure, nearly five times as high as a radiation worker's annual safe exposure limit.

Extended radiation exposure brings a risk of cancer and could also lead to eye cataracts, nervous-system damage, and problems with attention and memory.

But Bezos' and Musk's visions aren't so different yet

Despite the friction between Musk's and Bezos' visions of humanity's future in space, their immediate goal is the same: settle on the surface of the Moon.

"We should have a base on the Moon, like a permanently occupied human base on the Moon, and then send people to Mars," Musk said after the first launch of SpaceX's Crew Dragon spaceship. "That's what we should do."

Bezos said something similar in 2017, according to The Washington Post: "I think that if you go to the Moon first, and make the Moon your home, then you can get to Mars more easily."

But Bezos thinks that after settling on the Moon, it would make more sense to focus on populating the space around Earth. That's safer, he has said, because it's closer to home if any problems arise.

He also envisions energy generation and heavy industry moving into space, turning Earth into a realm of residences, parks, and light industry.

"But we also don't want to face a civilisation of stasis, and that is the real issue if we just stay on this planet. That's the long-term issue."

He added: "Everybody on this planet is going to want to be a first-world citizen using first-world amounts of energy, and the people who are first-world citizens today using first-world amounts of energy? We're going to want to use even more energy. A life of stasis would be population control combined with energy rationing … And that to me doesn't sound like a very exciting civilisation for our grandchildren's grandchildren."

Musk has not denied the risks of reaching for Mars and has often remarked on the endeavour's peril.

"The first journey to Mars is going to be really very dangerous. The risk of fatality will be high. There's just no way around it," Musk said in 2016.

"It would be basically: Are you prepared to die? And if that's OK, then you're a candidate for going."

But in Musk's line of thinking, such a risk is worth it to galvanize people to leave Earth for good.

"I think it would be the most inspiring thing that I can possibly imagine," Musk said of a crewed Mars mission. "Life needs to be more than just solving problems every day. You need to wake up and be excited about the future, and be inspired, and want to live."